What do you mean major distributions use evolution as the default email client ? AFAIK almost all major distros give you the choice of the desktop environment y

What do you mean major distributions use evolution as the default email client ? AFAIK almost all major distros give you the choice of the desktop environment you want if you want one. When you choose the gnome flavor of said distros, I suppose that it comes with evolution because it is the official default email client for gnome until its replacement, geary, is ready. But last time I checked in 2015 it was still in early stages of development despite having started circa 2012.